Photoflash control system



Deco 4, 1951 s HOFFMAN 2,577,683

PHOTOFLASH CONTROL SYSTEM Filed March 18, 1947 F2112 Z/f /j mam Patented Dec. 4, 1951 PHOTOFLASH CONTROL SYSTEM Paul S. Hoffman, Dayton, Ohio, assignor to Globe Industries, 1110., Dayton, Ohio Application March 18, 1947, Serial No. 735,376

3 Claims. I, l

The present invention relates generally to a system and apparatus for the automatic ignition of photographic flash lamps and is more particularly directed to such a system which is responsive to and is automatically operated by a sudden flash of light at a relatively remote point.

The present invention has particular utility in photographing large groups, such as gatherings in an auditorium or the like. The apparatus of the present invention may be placed at several points in the auditorium; and the photographic flash lamp in each such apparatus is discharged in response to the flash of a similar lamp which may be mounted on the camera. Thus, all portions of the auditorium are illuminated by the discharge of the flash lamps while the shutter is still open.

The present invention aims to provide a portable apparatus of this type which is compact, simple in construction and which is operable with a minimum of manipulation and without the necessity of any special skill or knowledge on behalf of the operator.

Another object of the present invention is to provide a system of this type which responds to a rapid change of light intensity but will remain inoperative at normal illumination of an auditorium.

Still another object of the present invention is to provide a control for the apparatus that .will render it equally effective under all conditions of ambient light intensity; another. aim of the present invention is to provide the ap- -paratus with control means to minimize the detail.

Essentially the present system comprises a photofiash bulb circuit controlled by a relay, the latter being disposed in an amplifier circuit, whose plate voltage is supplied by a manually variable potentiometer. A photocell is con- --nected to the grid of the amplifier to increase I the current therethrough when the photocell is exposed to a flash of light.

- 2 A pilot bulb is provided in parallel with the photofiash bulb receptacle. In use the potentiometer is preset, immediately prior to the insertion of the photoflash bulb in its receptacle, so that the pilot bulb just blinks out. This provides current in the operating circuit which is just short of the amount necessary to discharge the flash bulb; and consequently the system is sensitive, will act within only a few thousandths of a second, and the flash will be in substantial synchronism with the maximum aperture of the camera.

For a more detailed description of the present invention, reference is now had to the drawing which illustrates a preferred embodiment of the present invention; it being understood that variations thereof falling within the scope of the appended claims will be apparent to persons skilled in the art.

In the drawings the flash bulb I0 is shown disposed in the flash bulb receptacle II. The flash bulb l0 employed herein may be generally described as of the type which is discharged by a low voltage and low amperage. More particularly the photoflash lamp consists of a glass vessel filled with oxygen and contains aluminum v or magnesium in suitable form for rapid combustion. A low voltage filament, which may be coated with a combustible, initiates the combustion of the metal, when it is but slightly heated by a low voltage electric current.

The low voltage battery I2 is connected to the receptacle H by wire I3 relay switch I4, wires l5 and 16. The pilot light 29, which may be a miniature base 4.5 volt flashlight bulb is connected to wires 15 and I6 and is in parallel with the flash bulb receptacle H.

The switch I4 which controls the flash bulb and pilot light is operated by the relay IT. This relay is preferably a sensitive balanced armature type having a 2000 ohm winding and capable of operating on several milliamperes of current.

The amplifier l8, which may be an RCA-1S4, has its plate l9 connected to the relay IT by wire 20. The cathode or filament 2! is connected to battery 12 by means of switch 22.

The battery 23 (67.5 volts) supplies the necessary operating power to the system through the potentiometer 24 which includes the fixed resistance portion 25, preferably about 22,000 ohms, and the variable resistance 26 of about 2000 ohms, The wire 21 connects the cathode to the movable contact 28 which rides over the potentiometer and is manually movable thereon.

The switch is connected to switch 22 as indicated by dotted line 3| so that the two switches may be operated in unison. v

The photoelectric cell 33 has one of its electrodes connected to one side of the battery 23 by wire and its electrode is connected to control grid 31 of the amplifier 18 by wire 4|. The phototube load resistance 43 (about 1 megohm) is interposed between wire ll and the other side of the battery 23.

The variable voltage divider, or potentiometer 24 with its movable contact 28, controls or varies the grid bias as desired and at the same time serves to adjust the output of the amplifier circuit and additionally providesa means for pre' energizing or preloading the relay.

Essentially this voltage divider is employed so as to provide a current through relay II which is short of actuation of its switch 14, thereby permitting its subsequent actuation upon the illumination of photocell 33 with a minimum of delay. 7 r b v 'By the adjustment of the potentiometer by the movement of its movable contact 28, the bias or voltage level of the control grid 31 with respect to the filament 2| is varied. When the grid is made more positive the current in the output circuit, that is the current in relay I1, is increased. Thiscontrol thus provides an overriding of the biasing of the grid due to the photo- .tube, which biases in proportion to the mtensity diately before each use and uniform photographic results may thus be had. v I b The adjustment of the contact 28 on the potentiometer 26 alsoprovides for increasing the output of the amplifier l8 to a point just under the pull-on current of the relay l"l. This substantially eliminates or minimizes the time delay dueto the build-up time of I current inthe relay. By adjusting the potentiometer so that the relay H carries a current almost but not quite sulficient to close switch [4, and this without the effect of the remote flash bulb and with the phototube exposed to the ambient light of any value whatsoever, the remote flash bulb will then bring about the closing of the switch I 4 with a minimum delay. The currentnormally flowing through the relay I1 is less than, but not much less than the current required to actuate the relay.

During the life of the present apparatus the batteries I2 and 23 may deteriorate with time and thus vary the voltages normally existing in the system. This unknown variable is also compensated for or by-passed by the employment of the present potentiometer in the present system; vfor by the adjustment of contact 28 the optimum operating conditions are had over the full operating life of the batteries.

In use the present-apparatus is placed in the desired location in the room or auditorium so 303 closed the apparatus is ready for use and is at its maximum sensitivity.

Under some circumstances, such as when particularly sensitive operation is desired, means are provided, which limit and predetermine the amount of return movement of the movable contact 28. For this purpose the rotatable shaft carrying the movable contact 28 which travels over the resistance 26, also carries a freely rotatable disc like element 5} which has a pair of radial fingers 52 having their ends bent upwardly. These fingers are spaced only the amount necessary to provide the desired return movement of the movable contact 28. The contact 28 carried by the shaft is disposed between the two I upturned ends of the two fingers and has a substantial amount of free play between them such as about one eighth or one quarter inch or the like as desired. In operation, when the contact 28 is moved in the desired direction until pilot bulb 29 is illuminated, and- .duringthis movement the contact 28 engages one finger 52 on the disc and rotates the disc 5|. When the stop position is reached, that is when the bulb 29 is illuminated, the operator merely reverses the movement of contact 28 until it is stopped by or engages the other finger 52 on the disc 5|. Thus the amount of return movement of contact 28 is predetermined and is not made dependent upon the blinking out of bulb 29.

The quantitative values given in the present specification are merely illustrative, it being understood that these may be varied by persons skilled in the art. The specific types of theseveral devices employed herein are also for il- Iustrative purposes and may be replaced by other suitable and equivalent devices.

While the present invention is shown as specifically embodied in a photoflash apparatus, where it has particular utility, it will be understood that some phases of the present invention have more general application. Thus the employment of the voltage divider for controlling and enhancing the sensitivity of an amplifier circuit in the manner described herein may have application wherever it is desired to render such a system highly sensitive or where such control is desired.

What is claimed is: "1.111 an apparatus of the class described; a electric circuit including an amplifier tube hav-- ing a cathode, an anode, and a control electrode; an output circuit including said cathode and's'aid anode, a relay connected in series with said output circuit; a source of current, a voltage divider connected to said source, 'a portion of said voltage divider being connected to the "control electrode, variable means adjustable immediately before each use'for imposing a variable portion of said voltage divider upon the control electrode so as to permit adjustment of the current flowing in the-output circuit such that the current in the output circuit is slightly less than the current required to actuate the relay; and indicator means for use in adjusting said variable portion of the voltage divider, said indicator means being responsive to the relay being actuated for indicating whether or not the current flowing through the'output circuit is greater or less than thecurrent required to a'ctuatethe relay.

'2. In an apparatus 'for operating a photofiash bulb in response "to a remote flash of light, the.

'jcbfnbinafion i b il a source of electrical "enamplifier tube having a cathode, an anode and a control eIec'trodeJa'n output "circuit including said cathode and anode, a winding of an electromagnet connected in series with the output circuit, and a voltage divider connected to said source of energy, said voltage divider having one part connected in the output circuit and supplying voltage thereto, a second part of said voltage divider supplying bias voltage to said control electrode, variable means adjustable for ambient light conditions for adjusting said voltage divider to vary and adjust said voltages so as to normally cause a current to flow through the winding of the electromagnet, which current is slightly less than the current required to actuate the electromagnet, means in parallel with the voltage divider for energizing the control electrode, said last mentioned means being responsive to an increase in light intensity for energizing the grid to thereby cause an increase in the current in the output circuit so as to actuate the electromagnet, and circuit means including the source of energy, a switch closed by the armature of the electromagnet, a receptacle, and a photoflash bulb in the receptacle so that as the cur rent in the electromagnet increases to actuate the switch the circuit through the photoflash bulb is completed to cause a flash.

3. The apparatus set forth in claim 2 having a pilot lamp in the circuit means and in series with said switch and the source of energy.

PAUL S. HOFFMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

